JP3296038B2 - High frequency switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency switch for switching a signal path in a high-frequency circuit such as a digital portable telephone.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 2, a high-frequency switch is used in a transmission circuit TX in a digital cellular phone or the like.
It is used for switching the connection between the antenna ANT and the connection between the reception circuit RX and the antenna ANT, and is connected to the antenna ANT, the transmission circuit TX, and the reception circuit RX.

FIG. 3 shows a conventional high frequency switch 11. In FIG. 3, the transmission circuit TX includes a capacitor 12a
To the anode of the diode 14a. The anode of the diode 14a is connected to ground via a series circuit of a strip line 15a acting as a choke coil and a capacitor 12b.
The connection point between a and the capacitor 12b is connected to the control terminal 16 via the resistor 13a. A control circuit for switching the high-frequency switch 11 is connected to the control terminal 16. The cathode of diode 14a is connected to antenna ANT via capacitor 12c.

The antenna ANT has a capacitor 1
Strip line 15b is connected via 2c. The strip line 15b is connected to the receiving circuit RX via the capacitor 12d, and the connection point between the strip line 15b and the capacitor 12d is connected to the anode of the diode 14b. The cathode of the diode 14b is connected to the ground via a parallel circuit of the capacitor 12e and the resistor 13b, and forms the high-frequency switch 11.

The high-frequency switch 11 configured as described above
, A positive voltage is applied to the control terminal 16. This voltage is applied to the diodes 14a, 1
The diodes 14a and 14b are turned on because they function as a forward bias voltage with respect to 4b. At this time, the DC component is cut by the capacitors 12a, 12b, 12c, 12d, and 12e, and the voltage applied to the control terminal 16 is applied only to the circuit including the diodes 14a and 14b. Accordingly, since the strip line 15b is grounded by the diode 14b and resonates at the transmission frequency, and the impedance becomes almost infinite,
A transmission signal from the transmission circuit TX is transmitted to the antenna ANT via the capacitor 12a, the diode 14a, and the capacitor 12c without being transmitted to the reception circuit RX.

On the other hand, when receiving, the control terminal 16
The voltage application to is stopped. Therefore, the diode 14
a and 14b are turned off, and the signal received from the antenna ANT is transmitted to the capacitor 12c and the strip line 15
b, transmitted to the receiving circuit RX via the capacitor 12d,
It is hardly transmitted to the transmission circuit TX side. As described above, the high-frequency switch 11 can switch between transmission and reception by controlling the voltage applied to the control terminal 16.

[0007]

However, in the conventional high-frequency switch 11 described above, the control terminal 1
6, a positive voltage is applied, the diode 14a is turned on, and in a transmission state in which a transmission signal from the transmission circuit TX is transmitted to the antenna ANT through the diode 14a, transmission power is consumed by the forward resistance of the diode 14a. ,
When the power of the transmission signal is large, there is a problem that the power loss in the diode 14a increases and the diode 14a generates heat. For this reason, it is necessary to use a diode 14a having a small forward resistance and a large permissible power loss P _D. However, such a diode has a disadvantage that the shape is large and expensive.

The present invention has been made to solve such a problem, and has as its object to provide a small, inexpensive high-frequency switch with small power loss.

[0009]

In order to achieve the above object, according to the present invention, a transmission circuit, a reception circuit and an antenna are connected, and the connection between the transmission circuit and the antenna and the connection between the reception circuit and the antenna are provided. A high frequency switch for switching is connected between the transmitting circuit and the antenna, and has a length of 1/4 of a wavelength λ of a signal at a receiving frequency.
A first strip line that will be the a second strip line connected between the antenna and ground is connected between the antenna and the receiving circuit, the signal at the transmission frequency
Connecting a third strip line that will be 1/4 the length of the wavelength λ of a first diode having a cathode an anode connected to the transmitting circuit side is connected to the ground side, the cathode is in the receiving circuit side And a second diode having an anode connected to the ground side , wherein the first diode
And the ground, the residual inductance of the first diode
A first capacitor that forms a series resonant circuit with the
And the first capacitor resonates at the reception frequency.
The capacitance value is set so that the second die
Between the diode and ground, the residual
Second capacitor forming a series resonance circuit with the conductance
And the second capacitor is provided at the transmission frequency.
The capacitance value is set so as to resonate . Further, in the present invention, the first die
Diode and the transmission circuit, and the second diode and the
Specially, do not include a strip line between
Sign.

[0010]

According to the above arrangement, switching between transmission and reception can be performed without a diode on a transmission line for transmitting a transmission signal from the transmission circuit to the antenna.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the high-frequency switch according to the present invention will be described below with reference to the drawings. FIG. 1 shows a high-frequency switch 1. In FIG. 1, a transmission circuit TX is connected to an antenna ANT via a series circuit of a capacitor 2a, a strip line 5a, and a capacitor 2c. The connection point between the capacitor 2a and the strip line 5a is connected to the cathode of the diode 4a, and the anode of the diode 4a is connected to the ground via the capacitor 2b.
a to the control terminal 6a.

The connection point between the strip line 5a and the capacitor 2c is connected to the ground via the strip line 5b and connected to the receiving circuit RX via a series circuit of the strip line 5c and the capacitor 2d. The connection point between the strip line 5c and the capacitor 2d is connected to the cathode of the diode 4b, and the anode of the diode 4b is connected to the ground via the capacitor 2e and to the control terminal 6b via the resistor 3b. The switch 1 is configured.

The control terminals 6a and 6b have
A control circuit for switching the high-frequency switch 1 is connected. The length of the strip line 5a is 1/4 of the wavelength λ of the signal at the reception frequency , and the length of the strip line 5c is the length of the signal at the transmission frequency.
The length of the strip line 5b is λ of the wavelength λ, and the length of the strip line 5b is 1/2 of the sum of the lengths of the strip lines 5a and 5c. The resistors 3a and 3b are used to pass a constant current through the diodes 4a and 4b.

When transmitting using the high-frequency switch 1 configured as described above, a negative voltage is applied to the control terminal 6a and a positive voltage is applied to the control terminal 6b. This voltage becomes a reverse bias voltage for the diode 4a and a forward bias voltage for the diode 4b, so that the diode 4a is turned off and the diode 4b is turned on. Therefore, the strip line 5c is grounded by the diode 4b and resonates at the transmission frequency, and the impedance becomes almost infinite. Therefore, the transmission signal from the transmission circuit TX is hardly transmitted to the reception circuit RX side. The antenna A passes through the capacitor 2a, the strip line 5a, and the capacitor 2c.
Transmitted to NT.

On the other hand, when receiving, the control terminal 6a
And a negative voltage is applied to the control terminal 6b. This voltage becomes a forward bias voltage for the diode 4a and a reverse bias voltage for the diode 4b.
N, and the diode 4b is turned off. Therefore, the strip line 5a is grounded by the diode 4a and resonates at the reception frequency, and the impedance becomes almost infinite. Therefore, the reception signal from the antenna ANT is hardly transmitted to the transmission circuit TX side, and the strip line 5a is 2c, the strip line 5c, and the capacitor 2d, and transmitted to the receiving circuit RX.

The strip line 5b serves as a path for allowing a current to flow through the diodes 4a and 4b by the voltage applied to the control terminals 6a and 6b in terms of DC, and the strip line 5a in terms of AC. And has the function of increasing the impedance at the connection point of the strip line 5b and reducing the insertion loss.

The capacitors 2a, 2b, 2c, 2
d and 2e limit the current path so that the current flowing by the voltage applied to the control terminals 6a and 6b flows only to the circuit including the diodes 4a and 4b, so as not to affect other parts. It is. The capacitors 2b and 2e form a series resonance circuit with the residual inductances of the diodes 4a and 4b connected to the capacitors 2b and 2e, respectively. The capacitor 2b resonates at the reception frequency and the capacitor 2e resonates at the transmission frequency. Each capacitance value is set, and the impedance of each resonance circuit is reduced at the time of reception or transmission, so that the strip lines 5a,
5c is brought close to the ground potential to reduce insertion loss.

The high-frequency switch 1 thus configured
By controlling the voltage applied to the control terminals 6a and 6b, transmission and reception can be switched, and since a diode is not directly interposed on the transmission line of the transmission signal, power loss during transmission can be reduced. it can.

[0019]

As described above, according to the high-frequency switch of the present invention, since no diode is directly interposed on the transmission line of the transmission signal, the power loss during transmission can be reduced. Further, since it is not necessary to use a diode having a large allowable power loss PD, a small and inexpensive high-frequency switch can be configured. Also,
According to the high-frequency switch according to the present invention, the first and second
Capacitors connected to the first and second diodes
Form a series resonance circuit with the residual inductance of
The first capacitor resonates at the receiving frequency and the second capacitor
The capacitors are designed to resonate at the transmission frequency.
Since the capacity value is set, each time
Lower the impedance of the
Keep the strip line close to the ground potential to reduce insertion loss.
It also has the function of eliminating it.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a high-frequency switch according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating the operation of a high-frequency switch.

FIG. 3 is a circuit diagram of a conventional high-frequency switch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 High frequency switch 2a-2e Capacitor 3a, 3b Resistance 4a, 4b Diode 5a, 5b, 5c Strip line TX transmission circuit RX reception circuit ANT antenna

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-258126 (JP, A) JP-A-56-7526 (JP, A) Japanese Utility Model Showa 58-50750 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) H04B 1/44 H01P 1/15

Claims (2)

(57) [Claims] A high-frequency switch connected to a transmission circuit, a reception circuit, and an antenna for switching connection between the transmission circuit and the antenna and connection between the reception circuit and the antenna ; Week
A first strip line that will be the length of a quarter of a signal wavelength λ at a wave number, a second strip line connected between said antenna and ground is connected between the antenna and the receiving circuit, the transmission frequency Of the signal wavelength λ at
A third strip line that will be the length of 1/4, a first diode having a cathode an anode connected to the transmitting circuit side is connected to the ground side, the cathode is an anode connected to said receiving circuit side ground and a second diode connected to the side, between the first diode and ground, the first die
Form a series resonant circuit with the residual inductance of the ode
A first capacitor, wherein the first capacitor is
The capacitance value is set to resonate at the receiving frequency.
Cage, between the second diode and ground, the second die
Form a series resonant circuit with the residual inductance of the ode
A second capacitor, wherein the second capacitor is
The capacitance value is set to resonate at the transmission frequency
High-frequency switch, characterized in that there. 2. The first diode and the transmitting circuit,
And a switch between the second diode and the receiving circuit.
2. The method according to claim 1, wherein the trip line is not included.
The high frequency switch as described.